Commit 61989a80 authored by Nitin Gupta's avatar Nitin Gupta Committed by Greg Kroah-Hartman
Browse files

staging: zsmalloc: zsmalloc memory allocation library



This patch creates a new memory allocation library named
zsmalloc.

NOTE: zsmalloc currently depends on SPARSEMEM for the MAX_PHYSMEM_BITS
value needed to determine the format of the object handle. There may
be a better way to do this.  Feedback is welcome.
Signed-off-by: default avatarNitin Gupta <ngupta@vflare.org>
Signed-off-by: default avatarSeth Jennings <sjenning@linux.vnet.ibm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 17dd9f83
config ZSMALLOC
tristate "Memory allocator for compressed pages"
depends on SPARSEMEM
default n
help
zsmalloc is a slab-based memory allocator designed to store
compressed RAM pages. zsmalloc uses virtual memory mapping
in order to reduce fragmentation. However, this results in a
non-standard allocator interface where a handle, not a pointer, is
returned by an alloc(). This handle must be mapped in order to
access the allocated space.
zsmalloc-y := zsmalloc-main.o
obj-$(CONFIG_ZSMALLOC) += zsmalloc.o
/*
* zsmalloc memory allocator
*
* Copyright (C) 2011 Nitin Gupta
*
* This code is released using a dual license strategy: BSD/GPL
* You can choose the license that better fits your requirements.
*
* Released under the terms of 3-clause BSD License
* Released under the terms of GNU General Public License Version 2.0
*/
#ifdef CONFIG_ZSMALLOC_DEBUG
#define DEBUG
#endif
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/bitops.h>
#include <linux/errno.h>
#include <linux/highmem.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <asm/tlbflush.h>
#include <asm/pgtable.h>
#include <linux/cpumask.h>
#include <linux/cpu.h>
#include "zsmalloc.h"
#include "zsmalloc_int.h"
/*
* A zspage's class index and fullness group
* are encoded in its (first)page->mapping
*/
#define CLASS_IDX_BITS 28
#define FULLNESS_BITS 4
#define CLASS_IDX_MASK ((1 << CLASS_IDX_BITS) - 1)
#define FULLNESS_MASK ((1 << FULLNESS_BITS) - 1)
/*
* Object location (<PFN>, <obj_idx>) is encoded as
* as single (void *) handle value.
*
* Note that object index <obj_idx> is relative to system
* page <PFN> it is stored in, so for each sub-page belonging
* to a zspage, obj_idx starts with 0.
*/
#define _PFN_BITS (MAX_PHYSMEM_BITS - PAGE_SHIFT)
#define OBJ_INDEX_BITS (BITS_PER_LONG - _PFN_BITS)
#define OBJ_INDEX_MASK ((_AC(1, UL) << OBJ_INDEX_BITS) - 1)
/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
static DEFINE_PER_CPU(struct mapping_area, zs_map_area);
static int is_first_page(struct page *page)
{
return test_bit(PG_private, &page->flags);
}
static int is_last_page(struct page *page)
{
return test_bit(PG_private_2, &page->flags);
}
static void get_zspage_mapping(struct page *page, unsigned int *class_idx,
enum fullness_group *fullness)
{
unsigned long m;
BUG_ON(!is_first_page(page));
m = (unsigned long)page->mapping;
*fullness = m & FULLNESS_MASK;
*class_idx = (m >> FULLNESS_BITS) & CLASS_IDX_MASK;
}
static void set_zspage_mapping(struct page *page, unsigned int class_idx,
enum fullness_group fullness)
{
unsigned long m;
BUG_ON(!is_first_page(page));
m = ((class_idx & CLASS_IDX_MASK) << FULLNESS_BITS) |
(fullness & FULLNESS_MASK);
page->mapping = (struct address_space *)m;
}
static int get_size_class_index(int size)
{
int idx = 0;
if (likely(size > ZS_MIN_ALLOC_SIZE))
idx = DIV_ROUND_UP(size - ZS_MIN_ALLOC_SIZE,
ZS_SIZE_CLASS_DELTA);
return idx;
}
static enum fullness_group get_fullness_group(struct page *page)
{
int inuse, max_objects;
enum fullness_group fg;
BUG_ON(!is_first_page(page));
inuse = page->inuse;
max_objects = page->objects;
if (inuse == 0)
fg = ZS_EMPTY;
else if (inuse == max_objects)
fg = ZS_FULL;
else if (inuse <= max_objects / fullness_threshold_frac)
fg = ZS_ALMOST_EMPTY;
else
fg = ZS_ALMOST_FULL;
return fg;
}
static void insert_zspage(struct page *page, struct size_class *class,
enum fullness_group fullness)
{
struct page **head;
BUG_ON(!is_first_page(page));
if (fullness >= _ZS_NR_FULLNESS_GROUPS)
return;
head = &class->fullness_list[fullness];
if (*head)
list_add_tail(&page->lru, &(*head)->lru);
*head = page;
}
static void remove_zspage(struct page *page, struct size_class *class,
enum fullness_group fullness)
{
struct page **head;
BUG_ON(!is_first_page(page));
if (fullness >= _ZS_NR_FULLNESS_GROUPS)
return;
head = &class->fullness_list[fullness];
BUG_ON(!*head);
if (list_empty(&(*head)->lru))
*head = NULL;
else if (*head == page)
*head = (struct page *)list_entry((*head)->lru.next,
struct page, lru);
list_del_init(&page->lru);
}
static enum fullness_group fix_fullness_group(struct zs_pool *pool,
struct page *page)
{
int class_idx;
struct size_class *class;
enum fullness_group currfg, newfg;
BUG_ON(!is_first_page(page));
get_zspage_mapping(page, &class_idx, &currfg);
newfg = get_fullness_group(page);
if (newfg == currfg)
goto out;
class = &pool->size_class[class_idx];
remove_zspage(page, class, currfg);
insert_zspage(page, class, newfg);
set_zspage_mapping(page, class_idx, newfg);
out:
return newfg;
}
/*
* We have to decide on how many pages to link together
* to form a zspage for each size class. This is important
* to reduce wastage due to unusable space left at end of
* each zspage which is given as:
* wastage = Zp - Zp % size_class
* where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
*
* For example, for size class of 3/8 * PAGE_SIZE, we should
* link together 3 PAGE_SIZE sized pages to form a zspage
* since then we can perfectly fit in 8 such objects.
*/
static int get_zspage_order(int class_size)
{
int i, max_usedpc = 0;
/* zspage order which gives maximum used size per KB */
int max_usedpc_order = 1;
for (i = 1; i <= max_zspage_order; i++) {
int zspage_size;
int waste, usedpc;
zspage_size = i * PAGE_SIZE;
waste = zspage_size % class_size;
usedpc = (zspage_size - waste) * 100 / zspage_size;
if (usedpc > max_usedpc) {
max_usedpc = usedpc;
max_usedpc_order = i;
}
}
return max_usedpc_order;
}
/*
* A single 'zspage' is composed of many system pages which are
* linked together using fields in struct page. This function finds
* the first/head page, given any component page of a zspage.
*/
static struct page *get_first_page(struct page *page)
{
if (is_first_page(page))
return page;
else
return page->first_page;
}
static struct page *get_next_page(struct page *page)
{
struct page *next;
if (is_last_page(page))
next = NULL;
else if (is_first_page(page))
next = (struct page *)page->private;
else
next = list_entry(page->lru.next, struct page, lru);
return next;
}
/* Encode <page, obj_idx> as a single handle value */
static void *obj_location_to_handle(struct page *page, unsigned long obj_idx)
{
unsigned long handle;
if (!page) {
BUG_ON(obj_idx);
return NULL;
}
handle = page_to_pfn(page) << OBJ_INDEX_BITS;
handle |= (obj_idx & OBJ_INDEX_MASK);
return (void *)handle;
}
/* Decode <page, obj_idx> pair from the given object handle */
static void obj_handle_to_location(void *handle, struct page **page,
unsigned long *obj_idx)
{
unsigned long hval = (unsigned long)handle;
*page = pfn_to_page(hval >> OBJ_INDEX_BITS);
*obj_idx = hval & OBJ_INDEX_MASK;
}
static unsigned long obj_idx_to_offset(struct page *page,
unsigned long obj_idx, int class_size)
{
unsigned long off = 0;
if (!is_first_page(page))
off = page->index;
return off + obj_idx * class_size;
}
static void free_zspage(struct page *first_page)
{
struct page *nextp, *tmp;
BUG_ON(!is_first_page(first_page));
BUG_ON(first_page->inuse);
nextp = (struct page *)page_private(first_page);
clear_bit(PG_private, &first_page->flags);
clear_bit(PG_private_2, &first_page->flags);
set_page_private(first_page, 0);
first_page->mapping = NULL;
first_page->freelist = NULL;
reset_page_mapcount(first_page);
__free_page(first_page);
/* zspage with only 1 system page */
if (!nextp)
return;
list_for_each_entry_safe(nextp, tmp, &nextp->lru, lru) {
list_del(&nextp->lru);
clear_bit(PG_private_2, &nextp->flags);
nextp->index = 0;
__free_page(nextp);
}
}
/* Initialize a newly allocated zspage */
static void init_zspage(struct page *first_page, struct size_class *class)
{
unsigned long off = 0;
struct page *page = first_page;
BUG_ON(!is_first_page(first_page));
while (page) {
struct page *next_page;
struct link_free *link;
unsigned int i, objs_on_page;
/*
* page->index stores offset of first object starting
* in the page. For the first page, this is always 0,
* so we use first_page->index (aka ->freelist) to store
* head of corresponding zspage's freelist.
*/
if (page != first_page)
page->index = off;
link = (struct link_free *)kmap_atomic(page) +
off / sizeof(*link);
objs_on_page = (PAGE_SIZE - off) / class->size;
for (i = 1; i <= objs_on_page; i++) {
off += class->size;
if (off < PAGE_SIZE) {
link->next = obj_location_to_handle(page, i);
link += class->size / sizeof(*link);
}
}
/*
* We now come to the last (full or partial) object on this
* page, which must point to the first object on the next
* page (if present)
*/
next_page = get_next_page(page);
link->next = obj_location_to_handle(next_page, 0);
kunmap_atomic(link);
page = next_page;
off = (off + class->size) % PAGE_SIZE;
}
}
/*
* Allocate a zspage for the given size class
*/
static struct page *alloc_zspage(struct size_class *class, gfp_t flags)
{
int i, error;
struct page *first_page = NULL;
/*
* Allocate individual pages and link them together as:
* 1. first page->private = first sub-page
* 2. all sub-pages are linked together using page->lru
* 3. each sub-page is linked to the first page using page->first_page
*
* For each size class, First/Head pages are linked together using
* page->lru. Also, we set PG_private to identify the first page
* (i.e. no other sub-page has this flag set) and PG_private_2 to
* identify the last page.
*/
error = -ENOMEM;
for (i = 0; i < class->zspage_order; i++) {
struct page *page, *prev_page;
page = alloc_page(flags);
if (!page)
goto cleanup;
INIT_LIST_HEAD(&page->lru);
if (i == 0) { /* first page */
set_bit(PG_private, &page->flags);
set_page_private(page, 0);
first_page = page;
first_page->inuse = 0;
}
if (i == 1)
first_page->private = (unsigned long)page;
if (i >= 1)
page->first_page = first_page;
if (i >= 2)
list_add(&page->lru, &prev_page->lru);
if (i == class->zspage_order - 1) /* last page */
set_bit(PG_private_2, &page->flags);
prev_page = page;
}
init_zspage(first_page, class);
first_page->freelist = obj_location_to_handle(first_page, 0);
/* Maximum number of objects we can store in this zspage */
first_page->objects = class->zspage_order * PAGE_SIZE / class->size;
error = 0; /* Success */
cleanup:
if (unlikely(error) && first_page) {
free_zspage(first_page);
first_page = NULL;
}
return first_page;
}
static struct page *find_get_zspage(struct size_class *class)
{
int i;
struct page *page;
for (i = 0; i < _ZS_NR_FULLNESS_GROUPS; i++) {
page = class->fullness_list[i];
if (page)
break;
}
return page;
}
/*
* If this becomes a separate module, register zs_init() with
* module_init(), zs_exit with module_exit(), and remove zs_initialized
*/
static int zs_initialized;
static int zs_cpu_notifier(struct notifier_block *nb, unsigned long action,
void *pcpu)
{
int cpu = (long)pcpu;
struct mapping_area *area;
switch (action) {
case CPU_UP_PREPARE:
area = &per_cpu(zs_map_area, cpu);
if (area->vm)
break;
area->vm = alloc_vm_area(2 * PAGE_SIZE, area->vm_ptes);
if (!area->vm)
return notifier_from_errno(-ENOMEM);
break;
case CPU_DEAD:
case CPU_UP_CANCELED:
area = &per_cpu(zs_map_area, cpu);
if (area->vm)
free_vm_area(area->vm);
area->vm = NULL;
break;
}
return NOTIFY_OK;
}
static struct notifier_block zs_cpu_nb = {
.notifier_call = zs_cpu_notifier
};
static void zs_exit(void)
{
int cpu;
for_each_online_cpu(cpu)
zs_cpu_notifier(NULL, CPU_DEAD, (void *)(long)cpu);
unregister_cpu_notifier(&zs_cpu_nb);
}
static int zs_init(void)
{
int cpu, ret;
register_cpu_notifier(&zs_cpu_nb);
for_each_online_cpu(cpu) {
ret = zs_cpu_notifier(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
if (notifier_to_errno(ret))
goto fail;
}
return 0;
fail:
zs_exit();
return notifier_to_errno(ret);
}
struct zs_pool *zs_create_pool(const char *name, gfp_t flags)
{
int i, error, ovhd_size;
struct zs_pool *pool;
if (!name)
return NULL;
ovhd_size = roundup(sizeof(*pool), PAGE_SIZE);
pool = kzalloc(ovhd_size, GFP_KERNEL);
if (!pool)
return NULL;
for (i = 0; i < ZS_SIZE_CLASSES; i++) {
int size;
struct size_class *class;
size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
if (size > ZS_MAX_ALLOC_SIZE)
size = ZS_MAX_ALLOC_SIZE;
class = &pool->size_class[i];
class->size = size;
class->index = i;
spin_lock_init(&class->lock);
class->zspage_order = get_zspage_order(size);
}
/*
* If this becomes a separate module, register zs_init with
* module_init, and remove this block
*/
if (!zs_initialized) {
error = zs_init();
if (error)
goto cleanup;
zs_initialized = 1;
}
pool->flags = flags;
pool->name = name;
error = 0; /* Success */
cleanup:
if (error) {
zs_destroy_pool(pool);
pool = NULL;
}
return pool;
}
EXPORT_SYMBOL_GPL(zs_create_pool);
void zs_destroy_pool(struct zs_pool *pool)
{
int i;
for (i = 0; i < ZS_SIZE_CLASSES; i++) {
int fg;
struct size_class *class = &pool->size_class[i];
for (fg = 0; fg < _ZS_NR_FULLNESS_GROUPS; fg++) {
if (class->fullness_list[fg]) {
pr_info("Freeing non-empty class with size "
"%db, fullness group %d\n",
class->size, fg);
}
}
}
kfree(pool);
}
EXPORT_SYMBOL_GPL(zs_destroy_pool);
/**
* zs_malloc - Allocate block of given size from pool.
* @pool: pool to allocate from
* @size: size of block to allocate
* @page: page no. that holds the object
* @offset: location of object within page
*
* On success, <page, offset> identifies block allocated
* and 0 is returned. On failure, <page, offset> is set to
* 0 and -ENOMEM is returned.
*
* Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
*/
void *zs_malloc(struct zs_pool *pool, size_t size)
{
void *obj;
struct link_free *link;
int class_idx;